37. Counter-Strike (1999)
Counter-Strike is like the cancer of video games: If you don't get it out of your life early on, it will force you to undergo chemo and have a prolonged recovery. What we meant to say is that it will take over your life completely. Originally a mod to 1998's Half-Life, it is one of the most addictive multi-player experiences ever created. Attracting millions of players, it still has running servers for the more than a decade old title.